Pressure-casting apparatus



July 30, 1940. c. D. GALLowAY 2,209,882

PRESSURE-CASTING APPARATUS Filed Dec. s. 1958 WEA/mf?- F e. 40 m4/af 43afsbga// way Patented July 30, 1940 UNITED jsTATes PATENT "oFFlcl-JClaims.

In pressure-casting apparatus in which a vacuum is applied to the moldcavity just prior to forcing the molten metal'into the cavity bysuper-atmospheric pressure, it is important that the mold cavity shallbe' hermetically sealed against the entrance of air when the vacuum isapplied; and where the mold is in two or more parts which are broughttogether to close the mold cavity prior to the casting operation, it hasbeen found necessary to provide a gasket between the two confrontingparts of the mold'to effect an air-tight seal. Gaskets made of asbestosfabric or similar material resistant to heat in the form of a cord lyingin confronting grooves in the opposite faces of themold .have

been found unsatisfactory as they quickly becomev deformed and fail tomake an air-tight seal. To overcome this difficulty, applicant providesconfronting grooves in the opposite faces of the two parts of 'the moldto form a channel surrounding the mold'cavity at the parting line, intowhich channel molten metal is forced and solidified. For the initial'tests, this channel had a circular or similar cross-section but theshrinkage of the metal on cooling developed `suilicient space betweenthe surfaces of the gasket and the walls of the channel to permitleakage of air into the mold cavity when vacuum was applied. 'Iheimprovement was then devised whereby advantage is taken of the shrinkageof the metal on cooling tok increase the pressure between the surfacesof the gasket and the walls of the channel to perfect the seal. Ingeneral, this improvement consists in providing a channel whosecross-section has the form of two areas connected by a comparativelynarrow neck; or, in other y words, the periphery of the cross-sectionhas one or more re-entrant angles or equivalent're-en trant portionswhether angular or more or less cuved. Preferably one of the two areasas well as the neck should be comparatively small so that thecorresponding portion of themetal in the gasket will solidify first andwillthen be drawn, by the subsequent shrinkage of the larger area, intoclose contact with the surface4 of the channel in the mold where theseal is to be effected. l

In the accompanying drawing:

Fig. 1 is a diagram,'with parts in cross-section, showing the general.arrangement of the mold and the reservoir containing the molten metalfrom which the mold is illled.

Fig. 2 is a sectional view taken through the two-part mold. Y

Figs. 3, 4, 5 and 6 are cross-sections, on an,

enlarged scale, through alternative designs of the channel and gaskettherein, the'latter being exaggerated to illustrate the principleinvolved.

Fig. 7 is a cross-section, on an enlarged scale, showing the channel andgasket formed on one 5 side only of the parting-line of the mold.'

In Figs. 1 and 2, I represents one-half of the mold, the other half (notshown in Fig. l) being substantially identical except that the ducts foradmitting the molten metal and for applying 10 the vacuum need not beduplicated in the second half. 2 is a reservoir of molten metal in whichthe vessels 3 and 4 are submerged, the vessel 3 being designed to supplymolten metal to the mold cavity; and the vessel 4, which is identical l5with the vessel 3 being designed to supply molten metal to the gasketchannel surrounding the mold cavity. The design of the vessel 3 onlywill therefore be described .Aty the bottom of the vessel is a ballcheck valve 5 designed to permit 20 the molten metal to enter the vesselfrom the reservoir 2 but to prevent it from being forced back. -Thevessel is hermetically sealed except for the dip stand pipe 6- and theair supply pipe 1. 'I'he dip stand pipe 6 extends to a i aint nearl 25the bottom of the vessel 3 and is connected at its upper end tothe moldcavity through the duct or sprue 8. The vertical length of dip standpipe 6 is such that, when atmospheric pressure is applied to the surfaceof the .metal in the vessel 30 3 and vacuum is applied to the moldcavity, the differential pressure will not be suilicient to force themolten metalinto the mold butwill raise it only to some intermediatepoint as A in the stand pipe E. 35 The vessel 4 sconnected by va similarstand pipe 6a to the channel! which surrounds the mold cavity and intowhich the molten metal is A forced to provide an air-tight' gasket justprior to forcing the molten metal into the mold. Ihe mold is providedwith a vacuum chamber Il connectedto the mold cavity by vent ducts II,these vent ducts being of suchrestricted section that, while they-willpermit the air to escape from the mold cavity when vacuum is applied,they will 45 not permit the molten metal to pass into the vacuumchamber. Ihe vessels 3 and 4 are connected by pipes 1 and 1a,respectively, to a valve I2 by means of which connection may be madeeither to a source of compressed air via the pipe 5o I3 or to theatmosphere via the outlet I4.

p In operation, the mold is closed, the vacuum chamber I0 beingconnected to the source of vacuum with the valve I2 turned to connectthe.` pipes I and 'Ia to the atmosphere. This will K5 air to the pipe'la which rca-entrant angles cause the metal in pipe B to rise to thelevel A. The valve I2 is then turned to admit compressed will forcemolten metal into the gasket channel 8 where it will be prompt- 1ycongealed to form an air-tight seal around the mold cavity. The valve I2is then turned to admit compressed air to the pipe l which will forcethe molten metal through stand pi 6 into the mold cavity which hasalready exhausted of air through the vents Il and the vacuum chamber i0.'I'he valve I2 is then turned to shut of! the supply of compressed airand connect the pipes 1 and the mold is opened for 'removing the castingand the gasket, permitting the molten metal in the pipes G and 6a todrop to the level of the molten metal in the reservoir 2, thus'restoring the original conditions. l

- In Fig. 3 a design of channel and gasket is shown. comprising incross-section two similar areas 30 and 3i connected by the narrow neckv3,2, the shrinkage on cooling producing close contact at thepoints I3.

In Fig. 4 is shown the cross-section, to an enlarged scale. ofalpreferred design of channel and gasket. The cross-section of thechannel comprises a comparatively paratively small area 2l connected bya comparatively narrow^neck 22. The gasket. after solidifying, isrepresented in cross-section by the areas 20a and Zia connected byA theneck 22a. The shrinkage of the metal of the gasket, on cooling, hasdrawn the surfaces of the gasket .and the channel into close contact atthe points 23. The parting-line between the two-halves of the 'mold isindicated at P.

In Fig. 5 is shown a slight modiiication of the design shown in Fig. 4consisting in the `additional 55. producing additional points of contactpressure 56 due torshrinkage.

In Fig. 6 the cross-section of the gasket channel is shown. ascomprising the comparativelyv large ar'ea 60 with two relatively smallareas El, one on either side. connected to the area 60 by u the narrowneck B2.

In Fig. 7 the gasket channel is formed by a single groove on one sideonly of the parting-line P of the mold. and comprises in cross-sectionthe comparatively large area l0 and the comparativelvl small area Ilconnected by the narrow neck 42. -The contact pressure resulting fromshrinkage is produced at the points to eiect the seal.

The expression` "re-entrant angies. used in the claims is intended toinclude such re-entrant por'- thecross-section of thedefined by curvedlines (as tions of the periphery of gasket channel as are in Fig. 6), aswell as lines and sharp angles.

I do not intend to be limited save ofthe prior art and of the attachedclaims require. i i

I claim: 1. In a two-part mold adapted for use in a pressure-castingmachine having provision for applying vacuum to the mold cavity prior tofilling the mold, 'a groove in at least one of the confronting faces ofthe mold surrounding the mold cavity and providing, when the mold isclosed, a closed channel having a cross-section with at least one'peripheral 4re-entrant angle and adapted forcasting a metal gasket inwhich shrinkage of the congealed metal increases the those' dened bystraight as the scope sealing pressure between the surfaces of thegasket and the channel.

1a to the atmosphere, and A large Aarea 20 and a comperipheralre-entrant angle on each side of the parting-line and adapted forcasting a metal gasket. in which shrinkage of the congealed metalincreases the sealing pressure between the surfaces of the gasket andthe channel.

3. In a two-part mold adapted forI use in a pressure-casting machinehaving provision for applying a vacuum to the mold cavityprior tofilling the mold, confronting grooves in the confronting faces of themold surrounding the mold cavity and providing, when the mold is closed,a closed channel having a cross-'section comprising two areas connectedby a comparatively narrow neck, the parting-line. passing through bothareas and the neck and adapted for casting a metal gasket in whichshrinkage of the congealed metal increases the sealing pressure betweenthe surfaces of the gasket and the channel.

4. In a two-part mold adapted for use in a pressure-casting machinehaving provision for tween the surfaces of the gasket and the channel.

5. A multi-part mold for die casting having a mold cavity therein, asprue for admitting molten metal to said mold cavity, means for applyingvacuum to said mold cavity, said mold also having therein a secondcavity, normally empty, surrounding said mold cavity and adapted toreceive molten metal to form agasket surrounding said mold cavity andsealing the parting line thereof during the casting operation, and saidmold also having a second sprue therein for admittlng molten metaltosaid second cavity.

. 6. A multi-part mold for die casting having a mold cavity therein, asprue forming an inlet for molten metal to said mold cavity, means forapplying vacuum to said mold cavity, said mold .having asecond cavitytherein surrounding said mold cavity and adapted to receive molten metaltherein to form a gasket surrounding said mold cavity during casting,said second cavity having in cross-section two relatively large areascon- .,-nected by a portion of relatively small area.

7. A process of die casting comprising, casting a\gasket of metalsurrounding and spaced from the cavity of a multi-part mold to seal tothe parting-line of'said mold, applying a vacuum to the mold cavity ofsaid mold to exhaust said mold cavity, and filling said mold cavity withmolten metal to form a casting.

' 8. In the art of die casting, the improvement which consists in',supplying molten metal to a cavity in a multi-part mold surrounding themold cavity therein and causing said metal to congeal to form a gasketsealing-the parting-line of said mold cavity, evacuating gases from themold cavity by the application of vacuum while said cavity is connectedto a reservoir of molten metal subjected to atmospheric pressure andwhile said cavity is located at a height above said metal greater thanthat to which the metal will be raised by the pressure differentialbetween the atmosphere and the vacuum, and then introducing the metalinto the mold cavity by additional pressure/applied to the reservoir.

9. In the art of die casting, the improvement which consists in,introducing molten metal into a cavity in a multi-part mold, said cavitysurrounding and being spaced from the mold cavity of `said mold andcausing said metal to congeal and thereby form a gasket sealing thepartingline of` said mold cavity, evacuating gases from the mold cavityby the application of vacuum -while said cavity is connected to areservoir of molten metal subjectech to atmospheric pres-fl sure andwhile said :cavity is located at a height 3 above said metal greaterthan that to which the metal will be raised by the pressure diierentialbetween the atmosphere and the vacuum, then introducing the metalinto'the mold cavity by additional pressure applied tothe reservoir, andthen restoring atmospheric pressure to said reservoir andto the moldcavity to return to the reservoir` the surplus metal.

10. A process of sealing multi-part molds having a mold cavity thereinfor use in die casting into a cavity in said mold 'surrounding the moldcavity therein, and causing said metal to congeal and to press againstsurfaces of said cavity and to thereby seal the parting-line of saidmold cavity as by a gasket.

CHARLES D. GALLOWAY.

-by vacuum which comprises, filling molten metal

